Presently, almost all commercially available data storage systems use saturation recording and binary signaling schemes. Earlier data channels for storage systems utilized various forms of bit by bit peak detection. More recently, various forms of PRML (partial response maximum likelihood) or DFE (decision feedback equalization) have appeared in products. These improvements are still limited by the fact that the storage data channel is a saturation channel, and as such, has a significantly reduced information handling capacity compared to a linear data channel.
Recording media defects are currently mapped out at the factory and skipped under normal device usage, while remaining errors are corrected by error correction code. However, at higher aerial densities, defects in the media tend to become a greater problem.
The above-incorporated applications teach a linearization technique for linearizing magnetic recording channels without suffering signal to noise loss and not suffering bandwidth loss. Given this, the objective is to take the channel recording as close as possible to the theoretical capacity limit.
Spread spectrum communication systems are also known. As originally designed by actress Heddy LaMar and musician George Antheil and described in U.S. Patent xe2x80x9cSecret Communication Systemxe2x80x9d, U.S. Pat. No. 2,292,387 of Aug. 11, 1942, the frequency of the carrier was pseudo randomly changed in discrete steps to spread the spectrum at the transmitter. The received carrier frequencies were demodulated out by synchronization with the known transmitted pseudo random modulation to despread the spectrum. To a non-synchronized receiver, the spread spectrum signal looked like noise, but the intended receiver can despread the spectrum and recover the information. An added benefit to communication systems was robustness against narrow band jamming as well as atmospheric fading and multipath cancellations.
The present inventor has recognized that this communication system can be adapted to efficiently store linearized data in a magneto-optical storage system.
An efficient linearization of the saturation channel of a storage system is enabled by the techniques disclosed in the above-referenced application of Huber, Smith and Altman entitled xe2x80x9cEfficient Linearization of Saturation Channelsxe2x80x9d assigned to the assignee of this invention. The minimal loss of signal to noise ratio and no loss of bandwidth is achieved by this linearization process.
The novel system disclosed herein, based on spread spectrum techniques which have not previously been applied to recording systems, takes the incoming data stream and encodes it to N-parallel paths, each storing one/N of the incoming data rate. The system then orthogonally modulates each into spread spectra, and overlays each on the same frequency spectrum. This provides a bandwidth and signal to noise ratio efficiency of co-division multiple access systems. Moreover, robustness can be traded off against transmission efficiency by adjusting the number of coded layers of transmission.
This invention provides a means of maximization of data channel efficiency to near the theoretical capacity limits while simultaneously providing a means of increasing robustness against recording media defects. The invention enables a potential of as much as doubling of present product capacity without requiring an increase in the head-disc component performance; moreover, the robustness against defects in the media is increased.
Other features and advantages of the present invention will become apparent to a person of skill in the art who studies the present invention disclosure. Therefore, the scope of the present invention is to be limited only by the following claims.